// 実装 [1] だと禁止区間（左上と右下）へのトゲ配置を許容してしまうが
// そこに配置して ans=1 になるときは禁止区間以外への配置で ans=1 を達成できるので（未証明）
// 最小値の出力だけでは問題にならない（が復元付きだと多分死ぬ）
//
// 3x3 を 1x1 に縮約している
//   ↓
// ans=2 になるべきケースで禁止区間にトゲ配置して ans=1 にしてしまうので縮約は無理そう
// よって本実装では縮約しないで 1x1 のまま取り扱う実装にした
// 禁止区間へのトゲ配置を許容してしまう件は同じ
//
// [1] https://yukicoder.me/submissions/903569

// clang-format off
#ifdef _LOCAL
    #include <pch.hpp>
#else
    #include <bits/stdc++.h>
    #define cerr if (false) cerr
    #define debug_bar
    #define debug(...)
    #define debug2(vv)
    #define debug3(vvv)
#endif

using namespace std;
using ll = long long;
using ld = long double;
using str = string;
using P = pair<ll,ll>;
using VP = vector<P>;
using VVP = vector<VP>;
using VC = vector<char>;
using VS = vector<string>;
using VVS = vector<VS>;
using VI = vector<int>;
using VVI = vector<VI>;
using VVVI = vector<VVI>;
using VLL = vector<ll>;
using VVLL = vector<VLL>;
using VVVLL = vector<VVLL>;
using VB = vector<bool>;
using VVB = vector<VB>;
using VVVB = vector<VVB>;
using VD = vector<double>;
using VVD = vector<VD>;
using VVVD = vector<VVD>;
#define FOR(i,l,r) for (ll i = (l); i < (r); ++i)
#define RFOR(i,l,r) for (ll i = (r)-1; (l) <= i; --i)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) RFOR(i,0,n)
#define FORE(e,c) for (auto&& e : c)
#define ALL(c) (c).begin(), (c).end()
#define SORT(c) sort(ALL(c))
#define RSORT(c) sort((c).rbegin(), (c).rend())
#define MIN(c) *min_element(ALL(c))
#define MAX(c) *max_element(ALL(c))
#define COUNT(c,v) count(ALL(c),(v))
#define len(c) ((ll)(c).size())
#define BIT(b,i) (((b)>>(i)) & 1)
#define PCNT(b) ((ll)__builtin_popcountll(b))
#define LB(c,v) distance((c).begin(), lower_bound(ALL(c), (v)))
#define UB(c,v) distance((c).begin(), upper_bound(ALL(c), (v)))
#define UQ(c) do { SORT(c); (c).erase(unique(ALL(c)), (c).end()); (c).shrink_to_fit(); } while (0)
#define END(...) do { print(__VA_ARGS__); exit(0); } while (0)
constexpr ld EPS = 1e-10;
constexpr ld PI  = acosl(-1.0);
constexpr int inf = (1 << 30) - (1 << 15);   // 1,073,709,056
constexpr ll INF = (1LL << 62) - (1LL << 31);  // 4,611,686,016,279,904,256
template<class... T> void input(T&... a) { (cin >> ... >> a); }
void print() { cout << '\n'; }
template<class T> void print(const T& a) { cout << a << '\n'; }
template<class P1, class P2> void print(const pair<P1, P2>& a) { cout << a.first << " " << a.second << '\n'; }
template<class T, class... Ts> void print(const T& a, const Ts&... b) { cout << a; (cout << ... << (cout << ' ', b)); cout << '\n'; }
template<class T> void cout_line(const vector<T>& ans, int l, int r) { for (int i = l; i < r; i++) { if (i != l) { cout << ' '; } cout << ans[i]; } cout << '\n'; }
template<class T> void print(const vector<T>& a) { cout_line(a, 0, a.size()); }
template<class S, class T> bool chmin(S& a, const T b) { if (b < a) { a = b; return 1; } return 0; }
template<class S, class T> bool chmax(S& a, const T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> T SUM(const vector<T>& A) { return accumulate(ALL(A), T(0)); }
template<class T> vector<T> cumsum(const vector<T>& A, bool offset = false) { int N = A.size(); vector<T> S(N+1, 0); for (int i = 0; i < N; i++) { S[i+1] = S[i] + A[i]; } if (not offset) { S.erase(S.begin()); } return S; }
template<class T> string to_binary(T x, int B = 0) { string s; while (x) { s += ('0' + (x & 1)); x >>= 1; } while ((int)s.size() < B) { s += '0'; } reverse(s.begin(), s.end()); return s; }
template<class F> ll binary_search(const F& is_ok, ll ok, ll ng) { while (abs(ok - ng) > 1) { ll m = (ok + ng) / 2; (is_ok(m) ? ok : ng) = m; } return ok; }
template<class F> double binary_search_real(const F& is_ok, double ok, double ng, int iter = 90) { for (int i = 0; i < iter; i++) { double m = (ok + ng) / 2; (is_ok(m) ? ok : ng) = m; } return ok; }
template<class T> using PQ_max = priority_queue<T>;
template<class T> using PQ_min = priority_queue<T, vector<T>, greater<T>>;
template<class T> T pick(stack<T>& s) { assert(not s.empty()); T x = s.top(); s.pop(); return x; }
template<class T> T pick(queue<T>& q) { assert(not q.empty()); T x = q.front(); q.pop(); return x; }
template<class T> T pick_front(deque<T>& dq) { assert(not dq.empty()); T x = dq.front(); dq.pop_front(); return x; }
template<class T> T pick_back(deque<T>& dq) { assert(not dq.empty()); T x = dq.back(); dq.pop_back(); return x; }
template<class T> T pick(PQ_min<T>& pq) { assert(not pq.empty()); T x = pq.top(); pq.pop(); return x; }
template<class T> T pick(PQ_max<T>& pq) { assert(not pq.empty()); T x = pq.top(); pq.pop(); return x; }
template<class T> T pick(vector<T>& v) { assert(not v.empty()); T x = v.back(); v.pop_back(); return x; }
int to_int(const char c) { if (islower(c)) { return (c - 'a'); } if (isupper(c)) { return (c - 'A'); } if (isdigit(c)) { return (c - '0'); } assert(false); }
char to_a(const int i) { assert(0 <= i && i < 26); return ('a' + i); }
char to_A(const int i) { assert(0 <= i && i < 26); return ('A' + i); }
char to_d(const int i) { assert(0 <= i && i <= 9); return ('0' + i); }
ll min(int a, ll b) { return min((ll)a, b); }
ll min(ll a, int b) { return min(a, (ll)b); }
ll max(int a, ll b) { return max((ll)a, b); }
ll max(ll a, int b) { return max(a, (ll)b); }
ll mod(ll x, ll m) { assert(m > 0); return (x % m + m) % m; }
ll ceil(ll a, ll b) { if (b < 0) { return ceil(-a, -b); } assert(b > 0); return (a < 0 ? a / b : (a + b - 1) / b); }
ll floor(ll a, ll b) { if (b < 0) { return floor(-a, -b); } assert(b > 0); return (a > 0 ? a / b : (a - b + 1) / b); }
ll powint(ll x, ll n) { assert(n >= 0); if (n == 0) { return 1; }; ll res = powint(x, n>>1); res *= res; if (n & 1) { res *= x; } return res; }
pair<ll,ll> divmod(ll a, ll b) { assert(b != 0); ll q = floor(a, b); return make_pair(q, a - q * b); }
ll bitlen(ll b) { if (b <= 0) { return 0; } return (64LL - __builtin_clzll(b)); }
ll digitlen(ll n) { assert(n >= 0); if (n == 0) { return 1; } ll sum = 0; while (n > 0) { sum++; n /= 10; } return sum; }
ll msb(ll b) { return (b <= 0 ? -1 : (63 - __builtin_clzll(b))); }
ll lsb(ll b) { return (b <= 0 ? -1 : __builtin_ctzll(b)); }
// --------------------------------------------------------

// clang-format on
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);

    ll H, W;
    input(H, W);
    VS S(H + 2, str(W + 2, '#'));
    FOR (h, 1, H + 1) {
        FOR (w, 1, W + 1) {
            input(S[h][w]);
        }
    }

    const vector<int> dh4 = {0, 1, 0, -1};  // 右,下,左,上
    const vector<int> dw4 = {1, 0, -1, 0};

    auto on_grid = [&](int h, int w) -> bool { return (0 <= h && h < H + 2 && 0 <= w && w < W + 2); };
    auto on_grid2 = [&](int h, int w) -> bool {
        return on_grid(h, w) && not(h <= 3 && w <= 3) && not(H - 2 <= h && W - 2 <= w);
    };

    vector<vector<int>> dist(H + 2, vector<int>(W + 2, inf));
    deque<pair<int, int>> q;
    FOR (h, 4, H + 1) {
        dist[h][0] = 0;
        q.emplace_front(h, 0);
    }
    FOR (w, 1, (W - 3) + 1) {
        dist[H + 1][w] = 0;
        q.emplace_front(H + 1, w);
    }
    while (not q.empty()) {
        auto [h, w] = q.front();
        q.pop_front();
        for (int dh = -3; dh <= 3; dh++) {
            for (int dw = -3; dw <= 3; dw++) {
                if (abs(dh) + abs(dw) == 6) { continue; }
                int h2 = h + dh;
                int w2 = w + dw;
                if (not on_grid2(h2, w2)) { continue; }
                int cost = S[h2][w2] == '.';
                if (chmin(dist[h2][w2], dist[h][w] + cost)) {
                    if (cost == 0) {
                        q.emplace_front(h2, w2);
                    } else {
                        q.emplace_back(h2, w2);
                    }
                }
            }
        }
    }

    int ans = inf;
    FOR (w, 4, W + 1) { chmin(ans, dist[0][w]); }
    FOR (h, 1, (H - 3) + 1) { chmin(ans, dist[h][W + 1]); }
    print(ans);

    // REP (h, H) { debug(dist[h]); }

    return 0;
}